The present invention relates to an abnormal noise detector, and more particularly to a noise detector for use in determining the quality of gear units for automobiles and the like by detecting abnormal noises produced by the gear units.
In the manufacture of gear units for automobiles, the testing of the noise level of the gear unit is an important step in ascertaining its quality.
A low noise level is generally a sign of excellent mechanical performance. Although a noisy gear unit may in fact have excellent performance, a high noise level is often indicative of a short life span for the gear unit. In order to ensure a high quality gear unit of long life span, it is important to identify those gear units producing a high level of noise.
One of the conventional methods used to evaluate the noise level of a gear unit is to connect the gear unit between a drive motor and a load (for example, a second motor), drive the gear unit at various speeds, and have a trained human tester evaluate the noise level by listening. However, since the results vary depending on the expertise of the tester, his state of health at the time of testing, and other human factors, it has the disadvantage of low reproducibility.
Another conventional method of evaluating the noise level of gear units is to employ an automatic frequency analyzer instead of a human tester. In this method, a microphone placed in the vicinity of a gear unit to be tested is connected to the frequency analyzer. The gear unit is driven at different speeds, and the microphone picks up the noise from the gear unit and provides a corresponding electrical output to the frequency analyzer. The frequency analyzer automatically produces frequency spectra of the noise produced by the gear unit. From the frequency spectra, the frequencies of noise produced by the gear unit and the corresponding sound pressures can be determined. A frequency analyzer has the obvious advantage over a human tester in that its results are highly reproducible. However, the frequency of the noise produced by the gear unit is very dependent on the speed at which the gear unit is driven, and it is therefore necessary to obtain frequency spectra for the entire speed range of the gear unit. The evaluation of the large amount of data thus obtained is so time consuming that a faster determination of the overall noise level can be obtained by relying on the ear of a human tester than by evaluating the data. This method is far too time consuming to be used in testing mass produced gear units, in which speed is important.